As a total flow turbine of this type, there have generally been used impulse turbines. However, no highly efficient impulse total flow turbine has been developed yet. The reason for this is that the hot water being expanded in the nozzle is reduced to a two-phase fluid and such fluid is not transferred with high efficiency while it passes through the impulsive vane.
When saturated hot water having a pressure of 5 atmospheres is expanded to reach the atmospheric pressure and expected to change with substantially constant entropy, 91% by weight of the resultant is composed of water, and so 91% of the velocity energy is retained by the water, whereas the water vapor accounts for 99.4% of the total volume. As a result, although passage in the rotor vane is normally designed in consderation of the flow of water vapor accounting for 99.4% of the volume, water drops are not capable of joining the flow of water vapor which is deflecting at a small radius of curvature in the rotor vane, since the density of water is 1,659 times greater than that of water vapor and the water drops collide directly with the side wall of the rotor vane and flow as a thin viscous layer thereon and then out of the rotor vane. There is subsequently produced a significant difference in velocity between the water vapor and water flowing out of the rotor vane and thus their velocity triangles at the outlet of the rotor vane become entirely different from each other. This relation is shown in FIG. 7.
In FIG. 7, the solid and dotted lines, respectively, show the flow of water vapor and that of water drops within the total flow nozzle 1 and the impulse vane 2.
In FIG. 7, C.sub.1 denotes the velocity at the nozzle outlet, C.sub.2W and C.sub.2S the velocity at the rotor outlet of the water and steam, respectively, W.sub.1 the relative velocity at the rotor vane inlet, W.sub.2W and W.sub.2S the relative velocity at the rotor vane outlet of the water and steam, respectively, and u is the peripheral velocity of the rotor vane.
A study of the total flow impulse turbine based on the above consideration when an optimum velocity ratio is selected for the impulse turbine revealed from trial calculation that the efficiency of water, accounting for 91% of the total weight, reached only 38%, about half of the 74% of the water vapor. The overall efficiency of the total flow turbine became as low as about 42%.
Since a velocity coefficient of greater than 90% has been attained by the total flow nozzle when its dimensions and shape are suitably selected, the present invention attempts to make available a highly efficient total flow turbine stage by skillfully utilizing the above art, improving the rotor vane train and solving the aforementioned problems characteristic of the impulse total flow turbine. Since the problems related to the impulse total flow turbine, as mentioned above, result from causing a two-phase fluid composed of water and water vapor to deflect from the optimum flow path in the rotor vane to a large extent, the present invention is intended to make possible highly efficient power conversion with the least loss by improving the flow passage within the rotor vanes largely to prevent the two-phase fluid flowing in the passage inside the rotor vanes from producing water drops which collide with the rotor vane profile.